Method and device for socially aware model predictive control of a robotic device using machine learning

ABSTRACT

A computer-implemented method for determining a control trajectory for a robotic device. The method includes: performing an information theoretic model predictive control applying a control trajectory sample prior in each time step to obtain a control trajectory for a given time horizon; determining the control trajectory sample prior depending on a data-driven trajectory prediction model which is trained to output a control trajectory sample as the control trajectory sample prior based on an actual state of the robotic device.

CROSS REFERENCE

The present application claims the benefit under 35 U.S.C. 119 ofEuropean Patent Application No. 20190604.7 filed on Aug. 12, 2020, whichis expressly incorporated herein by reference in its entirety.

FIELD

The present invention relates to model predictive control for planningtrajectories of robotic devices.

BACKGROUND INFORMATION

For autonomous control of a robotic device, motion planning is used forefficiently accomplishing navigation tasks. Based on sensor inputs, anactual state of the robotic device and its environment are determined,while trajectories or motion paths, respectively, are developedconsidering also dynamic obstacles such as moving objects or individualsin the environment.

In general, model predictive control (MPC) is an efficient techniquewhich solves a receding horizon model-based open loop optimal controlproblem. Classical model predictive control techniques work well whenthe goal is the stabilization of constrained systems around equilibriumpoints or trajectories.

In G. Williams et. al., “Information theoretic MPC for model-basedreinforcement learning”, International Conference on Robotics andAutomation, 2017, an information theoretic approach is described toovercome some of the natural limitations of standard MPC techniques. Incontrast to standard MPC techniques, Information Theoretic ModelPredictive Control (IT-MPC) can work considering arbitrary systemdynamics and arbitrary nonlinear cost definitions.

SUMMARY

According to the present invention, a method for planning a trajectory,particularly for a robotic device, and a control unit and a roboticdevice according to the further independent claims are provided.

Further embodiments of the present invention are disclosed herein.

According to a first aspect of the present invention, acomputer-implemented method for determining a control trajectory for arobotic device is provided. In accordance with an example embodiment ofthe present invention, the method includes the steps of:

-   -   performing an information theoretic model predictive control        applying a control trajectory sample prior in each time step to        obtain a control trajectory for a given time horizon;    -   determining the control trajectory sample prior depending on a        data-driven trajectory prediction model which is trained to        output a control trajectory sample as the control trajectory        sample prior depending on an actual state of the robotic device.

In general, IT-MPC generates open-loop sequences of sampled controls byminimizing the Kullback-Leibler (KL) divergence between the currentcontrol distribution and the optimal one, derived by a desired costfunction. Control samples for the IT-MPC are generated by a normaldistribution centered around the previous control sequence. Therefore,this method performs well as long as the optimal control sequence onlychanges slightly from one step to the other.

However, if the optimal control sequence significantly changes, e.g.,due to a new goal location or an unexpected appearance of a dynamicobstacle, the local sampling around the previous control sequence maylead to a poor convergence to the optimal control sequence. Therefore,the standard IT-MPC tends to be inappropriate for navigation of mobilerobots in crowded environments.

Furthermore, the informed variant of theoretic model predictive controlmay iteratively evaluate a number of control trajectory samples derivedfrom control trajectory sample prior based on a given distribution ateach time step to obtain a further control trajectory sample, whereinthe further control trajectory sample is determined depending on acombination of the number of weighted control trajectory samples,wherein the weights are determined based on the costs of each of thenumber of control trajectory samples.

In accordance with an example embodiment of the present invention, itmay be provided that the data-driven trajectory prediction modelcomprises a neural network, particularly on the type of one of a softactor-critic network, a trust region network, a policy optimizationnetwork, a proximal policy optimization network, a deep deterministicpolicy gradients network.

One approach to overcome above limitation of the poor convergence to theoptimal control sequence is to use an informed sampling process byproviding a predicted control trajectory as a control trajectory priorusing a deep reinforcement learning algorithm. This may essentiallycomprise a data driven trajectory prediction model as machine-learningmodel which will generate a control trajectory prior based on a currentstate of the environment including a robot pose and poses of thedetected obstacles, wherein a pose includes a position and anorientation of the robot or a part of the robot within the environment.The data driven trajectory prediction model is trained to estimate thecontrol trajectory prior applying a training data set containingoptimized control trajectories for different states of the environment.The optimized control trajectories may be provided by any kind oftrajectory optimization processes for robotic devices in crowdedenvironments. Sampling from this control trajectory prior distributionleads to an improved performance since fewer samples fall in costlyparts of the state space.

In other words, one idea is to use an informed information-theoretic MPCapproach for trajectory planning in crowded environments in combinationwith a deep reinforcement learning approach. The trajectory predictionmodel which is trained and is to apply a network that can generate robotcontrol trajectories aware of the motions of surrounding dynamic objectsand/or individuals.

In general, the above example method improves the information theoreticmodel predictive controlled technique for locally generating robottrajectories by considering a stochastic non-linear system in dynamicenvironments. The obtained trajectories are a result of the KLdivergence minimization between the optimal sampling distribution andthe actual one.

A robotic device as understood herein includes a mobile robot, such asan autonomous cleaning robot, an autonomous lawn mower or the like, aswell as a robot having a movable manipulator, such as a robot arm, beingconfigured to be moved within a given space.

A trajectory as understood herein is a planned path of a motion arobotic device may move along or a part of a robotic device, such as amanipulator, may be moved.

Particularly, the above method uses a data-driven prediction model thatmakes use of the potential of the IT-MPC framework.

Moreover, the control trajectory sample prior may be obtained by themodelled control trajectory sample obtained by trajectory predictionmodel and the control trajectory sample obtained in the last time step.

Particularly, the control trajectory sample prior may be obtained by thesum of the modelled control trajectory sample obtained by the trajectoryprediction model and the control trajectory sample obtained in the lasttime step, particularly each weighted according to their trajectorycosts according to a given cost function. The cost of a trajectory maybe related to the expense to move along the trajectory in terms ofenergy, time, trajectory length and/or the like.

According to an example embodiment of the present invention, themodelled control trajectory sample may only be considered if thetrajectory costs of the modelled control trajectory sample is higherthan the trajectory costs of the control trajectory sample obtained inthe last time step.

According to an aspect of the present invention, a control unit, such asa data processing device, for determining a control trajectory for arobotic device is provided. In accordance with an example embodiment ofthe present invention, the control unit is configured to perform thesteps of:

-   -   performing an information theoretic model predictive control        applying a control trajectory sample prior in each time step to        obtain a control trajectory for a given time horizon;    -   determining the control trajectory sample prior depending on a        data-driven trajectory prediction model which is trained to        output a control trajectory sample as the control trajectory        sample prior based on an actual state of the robotic device.

According to a further aspect of the present invention, a robotic devicecomprises an actuation unit being configured to move the robotic deviceaccording to a control trajectory; and a control unit. In accordancewith an example embodiment of the present invention, the control unit isconfigured to perform the steps of:

-   -   performing an information theoretic model predictive control        applying a control trajectory sample prior in each time step to        obtain the control trajectory for a given time horizon;    -   determining the control trajectory sample prior depending on a        data driven trajectory prediction model which is trained to        output a control trajectory sample as the control trajectory        sample prior based on an actual state of the robotic device.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments of the present invention are described in moredetail below in conjunction with the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a mobile robot in a crowded environment, in accordance withan example embodiment of the present invention.

FIG. 2 shows a flowchart for an informed IT-MPC algorithm, in accordancewith an example embodiment of the present invention.

FIG. 3 shows a flowchart of a subroutine regarding the importancesampling weights function of the informed IT-MPC algorithm, inaccordance with an example embodiment of the present invention.

FIG. 4 shows a flow chart for the informed control function whichgenerates a control trajectory sample prior based on a trainedtrajectory prediction model, in accordance with an example embodiment ofthe present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 shows a system of a robotic device 1 as a mobile robot having atask to move through/within an environment E from position A to positionB along a planned trajectory. In the environment E dynamic objects 2, 3,4 may move performing their own tasks. The dynamic objects 2, 3, 4 maybe further mobile robots or individuals each showing a kind ofintelligent task driven behavior. The intelligent behavior of thedynamic objects 2, 3, 4 may follow a policy considering actions of therobotic device 1 and/or other dynamic objects 2, 3, 4.

The mobile robot may be an autonomous cleaning robot, an autonomous lawnmower, an autonomous service or care robot or the like. In otherembodiments, the robotic device may be a robot with a manipulator, suchas a robot arm, wherein the the manipulating device, such as a robotgripper, shall follow a planned trajectory.

The robotic device 1 may have a configuration as it is schematicallyshown in FIG. 1 . The robotic device 1 has a control unit 11 that isconfigured to perform the subsequently described method and to controlmovement of the robotic device 1 along a planned trajectory amongothers.

The control unit 11 may have a microprocessor or a microcontroller aswell as a memory for storing data and an algorithm code. Furthermore,the robotic device 1 has an actuation unit 12 for interaction with theenvironment, for instance the actuation unit 12 may include a tractionmotor for driving wheels of the robotic device 1 to move the roboticdevice 1 within the environment E. The actuation unit 12 may alsoinclude a controllable robot arm with a gripper or the like. Theactuation unit 12 is controlled by the control unit 11.

Furthermore, the robotic device 1 may include a sensor system 13 forsensing the environment E, particularly to detect other objects andstructures which may allow the localization of the robotic device 1 andof the dynamic objects 2, 3, 4 in the environment E such that theirpositions or their poses are known in the environment E. The sensorsystem 13 may include radar, Lidar, and/or imaging systems, such as oneor more cameras to scan the environment E surrounding the robotic device1.

When configuring such a robotic device 1, a control strategy has to beinstalled which allows the robotic device 1 to autonomously perform itstask in the environment E. The control strategy should have implementeda collision avoidance/handling to prevent motion trajectories where acollision with another dynamic object is likely or to cope withcollisions.

In simulation-based benchmarking of navigation algorithms for roboticdevices, it is generally difficult to effectively model the behavior ofthe dynamic objects 2.

This behavior of each of the dynamic objects may contribute to ordisturb the performing of the task of the robotic device 1.

Basically, in the control unit 11 of the robotic device 1, an informedinformation theoretic model predictive control (IT-MPC) approach isimplemented and performed. The informed information theoretic modelpredictive control (IT-MPC) process considers stochastic non-lineardiscrete time systems of the form of x_(t+1)=F(x_(t), v_(t)), wherex_(t)∈

^(n) is the system state at time t of dimension n. v_(t)∈

^(m) corresponds to the input control variable of dimension m with whitenoise obliged to nominal control u_(t) i.e. v_(t)=u_(t)+ε_(t) withε_(t)˜

(0,Σ), wherein (ν₀, ν₁, . . . , ν_(t) _(f) ⁻¹)=V∈

^(m×t) ^(f) corresponds to the input sequence and (u₀, u₁, . . . , u_(t)_(f) ⁻¹)=U∈

^(m×t) ^(f) to the input with its disturbance (ε₀, ε₁, . . . , ε_(t)_(f) _(−i))=ε.

The goal of IT-MPC is to solve the stochastic optimal control problem ofthe form

U * ≈ arg ⁢ min U ∈ 𝒰 ⁢ E U , ∑ ( ∑ t = 0 t f - 1 c ⁡ ( x t ) + ϕ ( x t f) + λ ⁢ u t - 1 T ⁢ ∑ - 1 u twhere

is the set of possible input sequences for the system, c(x_(t)) is astate-based cost, ϕ(x_(t) _(f) ) is a terminal cost and a rate λ>0. Theoptimal control distribution

*can be derived as

${q^{*}(V)} = {\frac{1}{\eta}{\exp\left( {{- \frac{1}{\lambda}}{S(V)}{p\left( {V{❘{0,\sum}}} \right)}} \right.}}$where S(V) denotes the state cost of an entire trajectory, p may be aGaussian with covariance Σ and η is a normalization factor. Toapproximate the above minimization problem, it is proposed to minimizethe KL divergence between the optimal control distribution

* and

_(U,Σ)U*≈argmin

_(KL)(

*,

_(U,Σ))

In case the optimal control distribution is Gaussian, the approximationis correct, and the resulting control trajectory is optimal. Givensamples V_(k) around a nominal control trajectory Û as described abovewith disturbances ε_(k) above approximative minimization problem can besolved by an importance sampling scheme

$U^{*} \approx {\hat{U} + {\overset{K}{\sum\limits_{k = 1}}{w_{k}\varepsilon_{k}}}}$where w_(k) are importance sampling weights. It is preferable to useabove formula as an update rule in an iterative manner.

A modified informed IT-MPC algorithm is described in conjunction withthe flow chart of FIG. 2 and the pseudocode as follows:

Algorithm: Informed IT-MPC algorithm.  1. Input: u*: Initial controlsequence, K: Number of samples, t_(f): Time horizon, F: Transitionmodel, ϕ, c: State cost, Σ, λ: Hyper-parameter, C decoder conditions  2. While task not completer do  3.  x₀ ← GetStateEstimate( )  4 .    U* ←InformControls (x0, u*, C, Σ, ϕ, c, F)  5.    for k ← 0 to K-1 do  6.  x ← x₀  7 .     S_(k) ← 0  8.   ε ← (ε₀ ^(k), ..., ε_(t) _(f) ⁻¹^(k)), ε_(t) ^(k) ∈

(0, Σ)  9.      For t ← 1 to t_(f): do 10      x ← F (x, u_(t−1) +(ε_(t−1) ^(k)) 11      $\left. S_{k}\leftarrow{S_{k} + {c(x)} + {\lambda u_{t - 1}^{T}{\sum\limits^{- 1}\varepsilon_{t - 1}^{k}}}} \right.$12       end for 13     S_(k) ← S_(k) + ϕ(x) 14     w_(k) ←ImportanceSamplingWeights(S_(k), λ) 15     $\left. U^{*}\leftarrow{U^{*} + {\sum\limits_{k\leftarrow 1}^{K}{w_{k}\varepsilon_{k}}}} \right.$16      end for 17      ApplyControl (u₀ ^(*)) 18      For t ← 1 tot_(f) − 1 do 19     u_(t−1) ^(*) ← u_(t) ^(*) 20.      end for 21.     u_(t) _(f) ⁻¹ ^(*) ← Initialize(u_(t) _(f) ⁻¹ ^(*)) 22 .  End while23.

According to step S1 (line 1), an initial configuration of parameters ofthe process is given. So, u* indicates an initial control sequence, K anumber of samples, t_(f) a time horizon, F a transition model, ϕterminal costs, c state costs, Σ,λ hyper-parameters and C decoderconditions.

A control loop is started in step S2 which is performed between lines 2to 22 of pseudocode of the Informed-IT-MPC algorithm which may beterminated once the goal state is reached by the robotic device 1.

In step S2 (line 3), the state of the system is obtained by the function“GetStateEstimate”. The state of the system may be determined byprocessing sensor signals to obtain a pose of the robotic device 1in/relative to the environment E and the poses and velocities of each ofdynamic obstacles 2, 3, 4 in the environment E as well known in the art.Basically, this is accomplished by reading the sensor signals such asLidar, radar and the like which are further processed to obtain therespective.

In step S3 (line 4), a control trajectory sample prior is obtained bythe algorithm “InformControls” which is described below in conjunctionwith FIG. 4 .

Based on the control trajectory sample prior U*, a loop between lines 5and 16 is performed for each of the samples k.

In step S4 (lines 6 to 8) x, S_(k) and ε_(k) are initialized.

In step S5, starting with the control trajectory prior U* as obtained instep S3, but in further iterations modified control trajectory prior U*,movement costs are predicted. This is performed by predicting futurestates of the system (line 10) with the time horizon t_(f), and thecorresponding movement costs S_(k) are accumulated (line 11). The soobtained movement costs are added to the terminal costs ϕ(x) in line 13.

In step S6 (line 14), importance sampling weights w_(k) are obtained byan algorithm “ImportanceSamplingWeights” as shown in the flowchart ofFIG. 3 and the following pseudocode:

Algorithm: ImportanceSamplingWeights (S_(k), λ).. 1: Input: S_(k), λ 2 :ρ ← min_(k) (S_(k)) 3 :$\left. \eta\leftarrow{\sum\limits_{k = 0}^{K - 1}{\exp\left( {{- \frac{1}{\lambda}}\left( {S_{k} - \rho} \right)} \right)}} \right.$4 : for k ← 0 to K − 1 do 5:  $\left. w_{k}\leftarrow{\frac{1}{\eta}{\exp\left( {{- \frac{1}{\lambda}}\left( {S_{k} - \rho} \right)} \right)}} \right.$6: end for 7 : return w_(k)

The importance sampling weights w_(k) are determined based on theaccumulated trajectory costs S_(k) of each control trajectory sample andthe given λ.

The function to determine the importance sampling weights uses theminimum costs ρ of all control trajectory samples considered so far instep S11 (line 2). In step S12 (line 3), a normalization factor

$\left. \eta\leftarrow{\overset{K - 1}{\sum\limits_{k = 0}}{\exp\left( {{- \frac{1}{\lambda}}\left( {S_{k} - \rho} \right)} \right.}} \right.$is calculated for making all movement costs of the considered samplescomparable. In step S13 (lines 4 to 6), importance sampling weightsw_(k) for each of the control trajectory samples (determined so far) areobtained depending on a difference between the respective controltrajectory costs S_(k) and the minimum control trajectory costs over allsamples. Loop of lines 4 and 6 is necessary, as only S_(k) is needed.

Basically, the importance sampling weights w_(k) are the higher, thehigher the difference between the control trajectory sample costs andthe minimum control trajectory sample costs ρ. The importance samplingweights w_(k) for S_(k) is returned to the Informed IT-MPC algorithm inline 7.

In step S7 (line15), based on the importance sampling weights w_(k), afurther control trajectory sample U* is obtained for the loop betweenlines 5 and 16.

In step S8 it is queried if all samples are considered. If positive(alternative: yes), the process is continued with step S9, otherwise(alternative: no) the process is continued with step S4.

In step S9 (line 17) of the informed IT-MPC algorithm, the first controldata (u*₀) is applied to the robotic device 1. The predicted trajectoryis updated to the following time step in step S10 (lines 18 to 20) sothat (u*₀) is set to the former U*₁ and so on.

In step S10 it is queried if the task is completed. If positive(alternative: yes), the process is ended, otherwise (alternative: no)the process is continued with step S2.

In step S3 (line 4), a control trajectory sample prior is obtained bythe algorithm which is described below in conjunction with FIG. 4 andthe following pseudocode:

Algorithm InformControls (u*, σ, φ₀, v₀, Σ, ϕ, q, F).  1: Input: u*, σ,φ₀, v₀, Σ, ϕ, q, F  2: û = DeepReinforcementLearning (σ, φ₀, v₀)  3: fort ← 1 to t_(f) do  4 :  {circumflex over (x)} = F(x, g (û_(t−1)) )  5: Ŝ_(k) = Ŝ_(k) + c({circumflex over (x)}) + λû_(t−1) ^(T) Σ⁻¹ û_(t−1) 6:  x* = F(x,g(u_(t−1)*))  7:  S_(k) ^(*) = S_(k)* + c(x*) +λu_(t−1)*^(T) Σ⁻¹ u_(t−1)*  8 : end for  9: Ŝ = Ŝ + ∅ ({circumflex over(x)}) 10: S* = S* + ∅(x*) 11: if Ŝ > S*then 12 :  $u^{*} = {{\left( {1 - \frac{\hat{S}}{\hat{S} +}} \right)\hat{u}} + {\left( {1 - \frac{\hat{S}}{\hat{S} +}} \right)u^{*}}}$13: end if 14 : return u*

The control trajectory sample prior u* is generated based on the actualstate of the system x, the trajectory control set of the last time stepu*, initial conditions needed by the network, such as some sensor inputsσ, the robotic device 1 current state φ₀, ν₀, a covariance metric Σ,terminal costs ϕ, state costs c and the transition model F.

In step S21 (line 2), a modelled control trajectory sample û isdetermined based on a data-driven trajectory prediction model (functioncall: DeepReinforcementLearning (σ, φ₀, ν₀)) which may be implemented asa machine learning model such as a neural network or the like. Inputsfor the trajectory prediction model are σ, φ₀, ν₀ indicating the actualstate of the system including the pose of the robotic device 1 and astate of the environment E.

The neural network can use different types, such as soft actor-critic,trust region, policy optimization, proximal policy optimization, deepdeterministic policy gradients or the like.

The trajectory prediction model is trained to generate the modelledcontrol trajectory sample based on the actual state of the system andhas been trained by optimized control trajectories. To obtain theoptimized control trajectories classical deterministic MPC techniquescan be used such as described in Schoels, T. et al., “An NMPC Approachusing Convex Inner Approximations for Online Motion Planning withGuaranteed Collision Freedom”, arXiv preprint arXiv:1909.08267, 2019.

In step S22 along the given time horizon, based on the actual state ofthe system x, the costs Ŝ of the modelled control trajectory sample ûpredicted by the trajectory prediction model including the respectiveterminal costs at the end of the time horizon is determined (lines 4, 5and 9)

In step S23 along the given time horizon, based on the actual state ofthe system x, the costs S* of the further trajectory control sample ofthe last time step u* including the respective terminal costs at the endof the time horizon is determined (lines 6, 7 and 10)

In step S24 (line 12), the control trajectory sample prior u* forreturning to step S4 of the main algorithm Alg1 is determined by acombination of the modelled control trajectory u and the furthertrajectory control sample u* of the last time step as determined in stepS7.

For instance, the returned control trajectory sample prior u* can begenerated from the lastly generated further control trajectory sample u*and the modelled control trajectory sample û. If the cost Ŝ of themodelled control trajectory sample û is higher than the costs S* of thelastly generated control trajectory sample u*, the returned controltrajectory sample u* is generated according to line 12 based on a sum ofthe weighted control trajectories, wherein the weights are generated bythe corresponding costs Ŝ and S*.

Otherwise the further control trajectory sample u* as determined by stepS7 of the main algorithm is used for the following iteration.

The above algorithm aims to find a control trajectory distribution thatminimizes the expected costs. The control trajectory distributiondepends strongly on the cost function and on the prediction of thetrajectory prediction model. The sampling-based approach is even moreaccurate, if the initial control trajectory sample distribution isalready close to the optimal one. Instead of a naïve initialization suchas a zero or constant velocity of the obstacles, the control trajectorysample distribution is guided towards low-cost areas of the state space.While using the data driven trajectory prediction model, controltrajectory samples may be generated that optimize the originalobjective.

What is claimed is:
 1. A computer-implemented method for determining acontrol trajectory for a robotic device, the method comprising thefollowing steps: performing an information theoretic model predictivecontrol applying a control trajectory sample prior in time steps toobtain the control trajectory for a given time horizon; determining thecontrol trajectory sample prior depending on a data-driven trajectoryprediction model which is trained to output a control trajectory sampleas the control trajectory sample prior based on an actual state of therobotic device; wherein the control trajectory sample prior is obtainedby a modelled control trajectory sample obtained using the trajectoryprediction model and the control trajectory sample obtained in a lasttime step; wherein the control trajectory sample prior is obtained as asum of the modelled control trajectory sample obtained by the trajectoryprediction model and the control trajectory sample obtained in a lasttime step, each weighted according to their trajectory costs accordingto a given cost function; wherein the modelled control trajectory sampleis only considered when the trajectory costs of the modelled controltrajectory sample are higher than the trajectory costs of the controltrajectory sample obtained in the last time step; and controlling therobotic device to act according to the determined control trajectory. 2.The method according to claim 1, wherein the information theoretic modelpredictive control iteratively evaluates a number of control trajectorysamples derived from the control trajectory sample prior based on agiven distribution at each time step to obtain a further controltrajectory sample, wherein the further control trajectory sample isdetermined depending on a combination of a number of weighted controltrajectory samples, and wherein weights of the weighted controltrajectory samples are determined based on costs of each of the numberof weighted control trajectory samples.
 3. The method according to claim1, wherein the data driven trajectory prediction model includes amachine learning mode, including a neural network, of a type of one of asoft actor-critic network, or a trust region network, or a policyoptimization network, or a proximal policy optimization network, or adeep deterministic policy gradients network.
 4. The method according toclaim 1, wherein the robotic device is controlled to act according tothe determined control trajectory.
 5. A control unit configured todetermining a control trajectory for a robotic device, the control unitconfigured to: perform an information theoretic model predictive controlapplying a control trajectory sample prior in time steps to obtain thecontrol trajectory for a given time horizon; determine the controltrajectory sample prior depending on a data driven trajectory predictionmodel which is trained to output a control trajectory sample as thecontrol trajectory sample prior based on an actual state of the roboticdevice; wherein the control trajectory sample prior is obtained by amodelled control trajectory sample obtained using the trajectoryprediction model and the control trajectory sample obtained in a lasttime step; wherein the control trajectory sample prior is obtained as asum of the modelled control trajectory sample obtained by the trajectoryprediction model and the control trajectory sample obtained in a lasttime step, each weighted according to their trajectory costs accordingto a given cost function; wherein the modelled control trajectory sampleis only considered when the trajectory costs of the modelled controltrajectory sample are higher than the trajectory costs of the controltrajectory sample obtained in the last time step.
 6. The control unit asrecited in claim 5, wherein the control unit is a data processingdevice.
 7. A robotic device, comprising: an actuation unit configured tomove the robotic device according to a control trajectory; a controlunit configured to: perform an information theoretic model predictivecontrol applying a control trajectory sample prior in time steps toobtain the control trajectory for a given time horizon; determine thecontrol trajectory sample prior depending on a data driven trajectoryprediction model which is trained to output a control trajectory sampleas the control trajectory sample prior based on an actual state of therobotic device; wherein the control trajectory sample prior is obtainedby a modelled control trajectory sample obtained using the trajectoryprediction model and the control trajectory sample obtained in a lasttime step; wherein the control trajectory sample prior is obtained as asum of the modelled control trajectory sample obtained by the trajectoryprediction model and the control trajectory sample obtained in the lasttime step, each weighted according to their trajectory costs accordingto a given cost function; wherein the modelled control trajectory sampleis only considered when the trajectory costs of the modelled controltrajectory sample are higher than the trajectory costs of the controltrajectory sample obtained in the last time step.
 8. A non-transitorymachine readable medium on which are stored instructions for determininga control trajectory for a robotic device, the instructions, whenexecuted by a computer, causing the computer to perform the followingsteps: performing an information theoretic model predictive controlapplying a control trajectory sample prior in time steps to obtain thecontrol trajectory for a given time horizon; determining the controltrajectory sample prior depending on a data-driven trajectory predictionmodel which is trained to output a control trajectory sample as thecontrol trajectory sample prior based on an actual state of the roboticdevice; wherein the control trajectory sample prior is obtained by amodelled control trajectory sample obtained using the trajectoryprediction model and the control trajectory sample obtained in a lasttime step; wherein the control trajectory sample prior is obtained as asum of the modelled control trajectory sample obtained by the trajectoryprediction model and the control trajectory sample obtained in a lasttime step, each weighted according to their trajectory costs accordingto a given cost function; wherein the modelled control trajectory sampleis only considered when the trajectory costs of the modelled controltrajectory sample are higher than the trajectory costs of the controltrajectory sample obtained in the last time step.
 9. The control unit asrecited in claim 5, wherein the control unit is further configured tocontrol the robotic device to act according to the determined controltrajectory.
 10. The non-transitory machine readable medium as recited inclaim 8, wherein the instructions, when executed by the computer,further cause the computer to perform the following step: controllingthe robotic device to act according to the determined controltrajectory.